This application claims the priority of PCT International No. EP00/10450 filed Oct. 24, 2000 and German Patent Document 19954689.4, filed Nov. 13, 1999, the disclosures of which are expressly incorporated by reference herein.
The present invention relates to a multi-cylinder internal combustion engine with at least one cylinder row and a cylinder head housing containing intake and exhaust valves that feed combustion air to the cylinders and release combustion exhaust gases through an exhaust system via control devices in dependence of the position of the crankshaft.
In multi-cylinder internal combustion engines the exhaust gases produced during the combustion process are released to the outside with the aid of manifolds which are allocated to the individual cylinders and then flow together into a joint exhaust manifold pipe. In the case of a predetermined firing order, operating conditions can occur where the opening phases of the exhaust valves of two cylinders that are arranged in one cylinder row overlap. This condition is particularly critical when the intake and exhaust valves of the first cylinder in the firing sequence are still in the overlapping opening phase. During the opening of the exhaust valve of the cylinder that fires later and thus exhausts later, the higher-pressure exhaust gas can reach the cylinder area of the cylinder that exhausts sooner. A high degree of residual gas with negative consequences on the knock limit as well as an insufficient cylinder filling rate with new gas are the result.
The utilization of variable control times reinforces the distribution of the individual cylinders air intake, and does so even more with a larger adjustable range. The reduction in the air intake of the disadvantaged cylinders can lead to a reduction in the air intake particularly for a crank angle (KW) of less than 100xc2x0, which diminishes the desired torque increase considerably.
It is therefore an object of the present invention to eliminate and/or reduce such negative consequences and to achieve a uniform optimal cylinder filling rate across the entire cylinder row of the internal combustion engine.
This object has been achieved with the present invention by providing that apparatus (44xe2x80x2) for generating differing exhaust valve lift progressions of at least two cylinders arranged in one cylinder row, leading to a reduction in the overlapping opening phases of these exhaust valves (28), where an intake valve (26) and an exhaust valve (28) of one of the at least two cylinders are in an overlapping opening phase.
By reducing the overlapping opening phases of the exhaust valves of cylinders that are arranged in one cylinder row, the exhaust lead thrust, which comes from the cylinder exhausting later and reaches the overlapping opening phase of the intake and exhaust valves of the cylinder exhausting sooner, is reduced. This results in a basically uniform new gas cylinder filling rate for all cylinders.
A reduction in the overlapping opening phases of exhaust valves that are allocated to the cylinders in one cylinder bank can easily be achieved by equipping the cams that are arranged on an exhaust cam shaft with different cam shapes.
A satisfactory bunching of the air intake curves for all cylinders across the entire r.p.m. range is created especially when the cylinders that are favored by the firing sequence are equipped with cams that have a smaller cam width than those cylinders where due to the firing sequence the exhaust lead thrust of the cylinder exhausting later in the cylinder row reaches the overlapping opening phase of the intake and exhaust valves of the cylinder exhausting sooner.
Optimization of the cylinders that are disadvantaged by the firing sequence is achieved when the narrower cam of the cylinder exhausting sooner has a cam width that is smaller by a crank angle of 10xc2x0 to 20xc2x0 per 1 mm valve lift.
Particularly on a V-8 engine with, for example, a 90xc2x0 bend of the crankshaft, where the engine experiences good balancing of masses and moments, the gas exchange disadvantages occurring particularly with this type of engine can be largely compensated for with the reduction in overlapping opening phases of the exhaust valves.
The gas exchange disadvantages on such internal combustion engines are particularly noticeable when the 4-finger exhaust manifold that is flanged on the exhaust side of the two cylinder banks transitions into a joint exhaust manifold pipe after a short distance. This type of exhaust gas discharge is beneficial because this way primary catalytic converters can be used and only one pre-catalytic converter and one lambda probe must be integrated into the exhaust manifold pipe that is provided for each cylinder row. Due to the short exhaust manifold pipes, however, the risk arises that the majority of the exhaust lead thrust from the cylinder exhausting later ends up in the cylinder exhausting sooner. On a V-8 engine with such an exhaust discharge, the gas exchange disadvantages can thus be fully compensated for so that impact of variable control times can fully take effect across the entire r.p.m. range, achieving the desired ample torque progression.